The present invention concerns chemical-mechanical polishing of semiconductor wafers or similar workpieces, and more particularly relates to a device for effectively containing an abrasive slurry on a rotating polish table.
In the conventional "chem-mech polish" (CMP) process, passivated semiconductor wafers are rotated against a polishing pad. A pH-controlled abrasive slurry introduced onto the rotating table maintains a proper etch rate of the passivation layer to achieve a very smooth planar surface on the wafers. U.S. Pat. No. 4,910,155 to Cote and Leach describes preferred procedures and materials for polishing semiconductor wafers; this patent also refers to other descriptions of "chem-mech" polishing methods.
In some CMP systems, the slurry flows continuously onto a flat polish table. As the table rotates, slurry is flung off the edge and carried away by a drain. This is wasteful of slurry material, leads to nonuniformity of the slurry at different locations, and splatters the abrasive slurry into surrounding machinery. In the Cote et al. patent, a raised wall of rectangular cross-section surrounds the table's edge. Such a wall or containment device must form a liquid-tight seal around the entire periphery of the polish table. Yet, at the same time, the wall must be easily removable in order to clean the polish table periodically, and must be quickly reinstallable on the table for setting up the next run with a new batch of slurry.
Conventional containment devices for CMP systems tend to be leaky, physically unwieldy, and difficult to install and remove. Some crude systems merely have as a wall, a thin plastic or metal band taped around the edge of a polish table. Large amounts of leakage occur in such systems, and cleaning the table between runs involves untaping and then replacing and resealing the entire wall. Another CMP apparatus uses a thick circular metal wall bolted at several points to counterbores in a flat polish table. Such a wall is bulky, but still weak and easily bent out of shape when removed from its polish table. Reinstallation for a new run requires accurate alignment and manipulation of a number of bolts. Leakage still occurs, however, between the table and the wall in the regions between the bolts.